我要做个无刷新dropdownlist的ajax联动，我的思路是这样的，
<asp:DropDownList ID="DropDownList1" runat="server" Width="88px" onchange="shengfen()">
然后再用XmlHttpRequest异步处理数据
JScript code:
function shengfen()
{
var dropID=document.getElementById("DropDownList1").value;
if(dropID=='--选择省份--')
{
document.getElementById("Label1").innerHTML="请选择省份!";
}
else
{
createXmlHttpRequest();
var url="ajaxdrop.aspx";
var postStr="ID="+dropID+"&Event=reg";
xmlHttp.open("Post",url,false);
xmlHttp.setRequestHeader("content-length","5000");
xmlHttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded;charset=utf-8");
xmlHttp.onreadystatechange=shengfenre;
xmlHttp.send(postStr);
}
}
再是这样的：（ajaxdrop.aspx.cs）这里不知道要怎么写？
C# code:
p ps = new p();
switch (Request.Form["Event"])
{
cas
